高红移处超大质量种子黑洞的形成与增长

Observations of high-redshift quasars reveal that some supermassive black holes (SMBH) with masses exceeding 1E9 solar mass formed as early as redshift z > 7. This means that some SMBHs had already formed about 700 million years after the Big Bang, raising the issue of how such SMBHs could grow so quickly. Currently, the only viable alternative to address this problem is the "direct collapse" scenario, where gas collapses within dark matter halos of 1E8 solar mass directly into the intermediate mass black hole (IMBH) with masses 1E6 solar mass as an SMBH seed. In early theoretical calculation, the gas in metal-free haloes with a virial temperature above 1E4 K flows towards the centre of the potential as a result of gravitational instabilities, forming a massive, pressure-supported central supermassive protostar. The high infall rate continues to compress and heat the core, and turns on hydrogen nuclear burning. After exhausting its hydrogen, the core of a protostar will contract and heat up until it suffers catastrophic neutrino losses and collapses to a black hole seed. ..Solution of the full problem requires application of the coupled radiative hydrodynamics of the collapsing matter, magneto-hydrodynamics (MHD), and other ingredients, and cannot be accomplished analytically. Models of the optically thin part of the collapse within DM haloes, on scales of 1 kpc down to 1 au, have emphasized various aspects of this stage: from formation and effects of molecular hydrogen, to Lyman alpha diffusion, to background UV flux produced by Population III stars. However, inside 1 au, the radiation pressure is expected to build up, and have both dynamical and thermodynamical effects. ..In our work we will test this assumption by treating the optically thick part of the accretion flow using radiative transfer in the flux-limited diffusion (FLD) approximation. In our model, we will model the formation of a protostar and evolve this protostar to much longer time until the gas collapse to the seed. During the collapse of the back hole seed, possible gravitational wave signal will also be calculated. After this work, we will also study the black hole feedback to its surrounding gas in the stage of the black hole seed growing from 1E6 to 1E9 solar mass. The accretion disk structure and accretion mode to the black hole will also be checked. Based on these results, we will calculate the radiative observation signature and provide theoretical support for the future observations.

在红移大于7的类星体的观测中，研究发现在这些类星体的中心存在着一个质量大于1E9太阳质量的黑洞。然而这些超大质量黑洞是如何在大约700万年的哈勃时间里形成，并快速增长的呢，这仍然是一个悬而未决的问题。我们将采用直接塌缩模型来解决高红移处超大质量黑洞的形成。通过数值模拟的方式，我们将模拟气体在一个1E8太阳质量的暗物质晕中直接塌缩到星系中心，并形成一个质量为1E6太阳质量的种子黑洞的过程。在该过程中，我们将求解气体的辐射转移方程，来了解气体塌缩到au尺度时，气体形成原恒星核的长时标演化过程。通过该计算，我们将了解原恒星核形成的物理状态，其吸积模式，并得到核球塌缩为种子黑洞的物理过程。当黑洞形成以后，我们还将模拟黑洞辐射对周边气体的反馈影响，然后得到种子黑洞从1E6到1E9太阳质量的增长过程。最后我们将计算黑洞在形成过程中不同阶段的观测特征，以期望为将来的观测计划提供理论支持。

在观测中，研究人员发现在红移约为7的时候，宇宙中存在着大量的高光度活动星系核以及超大质量黑洞。那么这些超大质量黑洞是如何在这么短的时间内形成的是一个需要解决的问题。我们通过数值模拟的方法研究在直接塌缩模型中，质量为1E6太阳质量的种子黑洞是如何形成的，形成过程是怎样的。我们研究的研究内容包括三方面：1). 直接塌缩模型生成种子黑洞的条件，2). 种子黑洞增长过程的反馈影响。3).种子黑洞形成过程的Lya辐射特征。我们建立了一个新的连接氢分子以及H-的相关性，当给定背景辐射光谱在Lymann-Werner波段的光谱以及辐射强度，我们建立的相关性即可给出直接塌缩模型的可能性。 我们通过数值方法，以及辐射转移方法，计算种子黑洞的反馈影响。我们发现吸积气体所产生的辐射在吸积盘的上方会产生较强的外流。外流不断的向外扩张，并催出一个空腔区域funnnel。外流会截断吸积过程，但吸积过程会快速的重新形成，结果就是吸积过程并未受到影响，即反馈机制并不能影响种子黑洞的增长过程。然而外流产生的空腔区域funnnel对Lya辐射的逃逸过程具有很大的影响。我们计算了Lya逃逸出来的谱线形状以及逃逸率，结果发现Lya是可以逃逸出来并被观测到的。